Machine control circuit

ABSTRACT

A control circuit for a press is arranged for requiring an operator to hold control buttons depressed for more than one complete press cycle before it will run in a continuous mode.

United States Patent Freeland I [54] MACHINE CONTROL CIRCUIT [72] Inventor: Edward J. Freeland, Hastings, Mich.

[73] Assignee: Gulf 8: Western Industrial Products Company, Salem, Ohio [22] Filed: Sept. 23, 1971 211 App]. No.1 183,202

[52] US. Cl. ..3l8/447, 307/141 [51] Int. Cl. .1102]! 15/00 [58] FieldofSearch...307/141, 141.4, 142; 317/123;

[56] References Cited 9 UNITED STATES PATENTS 3,249,820 5/1966 Stimmel ..307 /1 41x [4 1 Oct. 24,1972

3,004,202 10/1961 Simson ..31s/447x 2,951,192 8/1960 Feldhausen ..318/210X 2,947,930 8/1960 Feldhausen ..31s/447 x Primary ExaminerBer-nard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr. Attorney-Meyer, Tilberry and Body [57] nsmc'r A control circuit for a press is arranged for requiring an operator to hold control buttons depressed for more than one complete press cycle before it will run in a continuous mode.

. Claim 1 i -9m .7 6,

PRESS 1. MACHINE CONTROL CIRCUIT BACKGROUND OF THE INVENTION This application pertains to the art of machine controls and more particularly to a control arrangement for a machine having a reciprocating member. The instroke operating mode, the operator of the press is usually putting his hands in the die area of the press for inserting and removing workpieces. The control circuit includes a pair of pushbuttons which the operator must hold depressed over a predetermined portion of the slide stroke before the press will continue to run after the buttons are released. For example, if the operator is required to hold the buttons depressed until the slide is almost down, hecannot accidentally put his hands in the die area before the die is closed. Once the operator releases the pushbuttons, he can prepare to remove and insert another workpiece as the slide moves up. In the single stroke operating mode, the slide will then automatically stop at its topmost position and the operator is again required to hold the pushbuttons depressed for another press cycle. i

In the continuous operating mode, conventional circuits simply require the operator to hold the pushbuttons depressed for a predetermined portion of the first slide stroke and the press will then run continuously after the pushbuttons are released. This arrangement presents a serious hazard to an operator. An operator, who is unaware that the continuous run switch has been thrown, will depress the pushbuttons for a predetermined portion of the first slide stroke and assume the press is inits single stroke mode. The operator will then release the pushbuttons and place his hands in the die area to remove and insert a workpiece as the slide moves up. With-the press in its continuous run mode, the slide will not stop at top and will rapidly move back down. This may cause serious injury to the operator.

SUMMARY OF THE INVENTION A control circuit is provided for a machine having a reciprocating work performing member which reciprocates between first and second positions. The work performing member moves in cycles, with one cycle being defined by movement from the first position to the second position and back to. the first position. The circuit includes pushbutton means for energizing the machine to reciprocate the work performing member; The pushbutton means is removable between a released position and a depressed position.

In accordance with the preferred arrangement, the circuit includes holding circuit means for continuously energizing the machine to continuously reciprocate the work performing member in repetitive cycles. The circuit includes locking means for locking in said holding circuit. The locking means isenergized by holding the pushbutton means in its depressed position while the work performing member moves through more than member moves from the first position to the second position at least two times.

In accordance with one arrangement, locking means includes first and second relay means, and first and second limit switch means. The first limit switch means closes to energize the first relay means during a first cycle of the work performing member. The second limit switch means closes to energize the second relay means during a second cycle of the work performing member. In the most preferred arrangement, the

second limit switch means closes to energize the second relay means only after the work performing member has moved from its first position to its second position at least two times. The first relay means has normally open contact means'in series with the second limit switch means and with the second relay means. The first relay means also has normally open contact means in parallel with the first limit switch means and in series with the first relay means. The second relay means further has normally open contact means in parallel with the second limit-switch means and in series with the second relay means.

In. one arrangement, solenoid means is provided for energizing a valve to a brake-clutch uniton a press. Both the first and secondrelay means include normally open contact means in series with the solenoid means in the holding circuit. v

With the arrangement of the present invention, an operator cannot be accidentally injured if he mistakenly assumes that the control circuit is in the single stroke mode. For example, if an operator assumes that the control circuit is in its single stroke mode when it is actually in its continuous run mode,'he will depress the pushbuttons for a portion of the first cycle and then release them preparatory to placing his hands in the die areafor removing or inserting a workpiece. As the slide moves up, the operator will have his hands in the die area and the slide will stop in its uppermost position. Arranging the control circuit so that the operator must continuously depress the pushbuttons for at least two die closures provides a manner in which the operator can easily check the mode the circuit is in and also minimizes the changeofinjury.

It is a principle object of the present invention to provide an improved control circuit for a machine having a reciprocating work performing member.

Itis another object of the present invention to provide an improved control circuit which requires an operator to maintain pushbuttonsdepressed for more than one cycle of a reciprocating work performing member before a machine will run in a continuous mode.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of anelectrical control circuit embodying the present invention; and

FIG. 2 is a graphical illustration of the condition and 1 operating points for limit switches in the circuit of FIG. 1 with respect to the position of a press slide. I

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 shows press A having a reciprocating slide driven by motor M through flywheel F and brakeclutch unit BC. Motor M is supplied with power through main circuit braker G from main lines L-l, L-2 and IJ-3. A control circuit H for press A is supplied with power through transformer I connected with lines L-1 and L-3. Air pressure is supplied to brake-clutch unit BC through solenoid valve J which is selectively opened by solenoids located in control circuit H.

A main on-off switch 42 for control circuit H is located in line 1. Stop and start switches 44 and 46 are located in line 4 in series with a forward and reverse motor control switch 48 having contact 50 located in line 4 and contact 52 located in line 5. A bar-run switch 54 has contact 56 in line 4, contact 58 in line 8, contact 60 in line 21 and contact 62 in line 33. When switch 54 is in its bar position, contacts 56 and 58 are open, while contacts 60 and 62 are closed. Thus, lines 4 and 8 are open so that energy cannot be supplied to motor control switch 48. Lines 21 and 33 are closed so that energy is directly supplied to solenoids 64 and 66 located in lines 19 and 31 respectively. This maintains solenoid valve J open so that the clutch or brake clutch unit BC is engaged but motor M is not running. In the event the press slide is stuck or 'a small adjustment is desired, a large metal bar may then be placed in flywheel F in order to manually turn flywheel F and move the slide.

For normal press operation, bar-run switch 54 is thrown so that contacts 56 and 58 are closed, while contacts 60 and 62 are open. With switches 44 and 46 closed, and contacts 50 and 56 closed, energy is supplied to relay MF through normally closed contact MR-l of relay MR. Energization of relay MF opens normally closed contact MF-l in line so that relay MR cannot be energized. Energization of relay MF also closes normally open contacts MF-2, MF-3, and MP4 located in lines 1.1-1, L-2 and L-3 so that motor M will run in a forward direction. Energization of relay MF also closes normally open contact MF-S in line 5 to establish a holding circuit so that momentary start button 46 can be released.

To run motor M in'a reverse direction, switch 48 is thrown so that contact 50 is open and contact 52 is closed. Relay MR is then energized through normally closed contact MF-l and contacts 52. Energization of relay MR opens normally closed contact MR-l so that relay MF cannot be energized. Energization of relay MR also closes normally open contacts MR-2, MR-3 and MR-4 to reverse the direction of current flow in the windings of motor M so that motor M will run in a reverse direction. Energization of relay MR also closes normally open contacts MR-S in line 6 to establish aholding circuit pass momentary; start button 46.

Aside from lines 21 and 33 which supply energy directly to solenoid 64 and 66 when switch 54 is in its bar position, the remainder of the control'circuit to be described is supplied with energy through line 8 which has a normally closed emergency stop button therein. Opening emergency stop button 70 at any point during operation of the press when it is in its run condition will immediately de-energize the remainder of the control circuit so that solenoid 64 and 66 become de-energized to close valve J and apply the brake of brake-clutch unit BC and stop movementof the slide in press A.

Run-jog push button 74 has normally closed contact 76 in line 14, normally open contact 78 in line 15 and normally open contact 80 in line 18. Run-jog pushbutton 84 has normally closed contact 86 in line 26, normally open contact 88 in line 27 and normally open contact 90 in line 30. A run-jog switch 92 has contact 94 in line 12, contact 96 in line 18, contact 98 in line 24 and contact 100 in line 30. When switch 92 is thrown to its jog position, contacts 94 and 98 are open, while contacts 96 and 100 are closed. Manually depressing pushbuttons 74 and 84 then closes contacts 80 and 90 in lines 18 and 30 respectively for supplying energy directly to solenoid valves 64 and 66 so that valve J will remain open and the clutch will be engaged. Pushbuttons 74 and 84 may then be bumped to inch or jog the press slide to a desired position. With switch 92 in its run condition, contacts 94 and 98 in lines 12 and 24 are closed, while contacts 96 and 100 in lines 18 and 30 are open.

A single stroke and continuous run switch 104 has contact 106 in line 12, contact 108 in line 19, contact 110 in line 20, contact 112 in line 24, contact 114 in line 31 and contact 116 in line 32. With switch 104 thrown to its single stroke position, contacts 106, 1 10, 112 and 116 are open, while contacts 108 and 114 are closed. With switches 54 and 92 thrown to their run position, and with switch 104 thrown to its single stroke position while motor M is running, a circuit is established in line 14 to relay R-l through contact 76, normally closed contact 1R-2 of relay R-2 and normally closed contact 1R-3 of relay R-3.

Energization of relay R-1 closes normally open contacts lR-l in line 13, 2R-1 in line 15 and 3R-1 in line 20. A circuit is also established in line 26 to relay R-4 through contact 86, and normally close contacts 1R-5 and 1R-6 of relays R5 and R-6.

Energization of relay R-4 closes normally open contacts 1R4 in line 25, 2R4 in line 27 and 3R-4 in line 32. Limit switches LS-l and LS-3 in lines 13 and 25 respectively then establish holding circuits through lines 13 and 25 to relays R-1 and R-4. As shown in FIG. 2,limit switches LS-l and LS-3, which are operated by the press slide, are closed for around the first 210 of slide stroke. A top stop pushbutton 120 has normally closed contacts 122 in line 15 and 124 in line 27 for reasons which will be further explained.

Depressing pushbuttons 74 and 84 will then begin operation of press A by energizing solenoids 64 and 66. A circuit is then established to relay R2 in lines 15 and 16 through contacts 78, 2R-1, 122 and normally closed contact 6R-7 of relay R-7. Energization of relay R-2 opens normally closed contact 1R-2 in line 14, and closes normally open contacts 2R-2 in line 12, 3R-2 in line 15, 4R-2 in line 17 and 5R-2 in line 27. A circuit is also established in lines 27 and 28 to relay R-5 through contact 88, contact 2R-4, contact 124, normally closed contact 1R-8 of relay R--8 and contact 5R2. Energization of relay R5 opens normally closed contact IRS in line 26, and closes normally open contacts 2R5 in line 24, 3R5 in line 27 and 4R5 in line 29.

Relay R3 is then energized through closed contact 4R2 in linel7. Energization of relay R3 opens normally closed contact 1R3 in line 14, and closes normally open contacts 2R3 in line 11, 3R3 in line 19, 4R3 in line 19, 5R3in line 23, 6R3 in line 31 and 7R3 in line 31.

Closing of .relay 4R5 in line 29 energizes relay R6. Energiz'atio'n or relay R6 opens normally closed contact 1R6 in line 26, and closes normally open contacts 2R6 in linel'l, 3R6 in 4R6 in line 19, 5R6 in line 23, 6R6 in line 31' and 7R6 in line 31.

Energization of the relays as described with pushbutton 74 held depressed then establishes a circuit to solenoid 64 through lines 12, 14, 15,17 and 19. Solenoid 166 is also energized through lines 24, 26, 27, 29 and 31. Solenoid valve J will then be open for supplying air pressure to brake-clutch unit'BC so that the clutch will beengaged and the press slide will be driven. lf pushbuttons 74 and Marc released at this point, solenoid valves 64 and 66 will be de-energized due to opening of contacts 78 and 88 in lines and 27. In order to keep the slide moving, pushbuttons 74 and 84 must be held depressed until the slide has traveled around 140 as indicated by distance X in FIG. 2. Once the slide has traveled that distance, limit switches LS2 and LS4 in lines 19 and 31 close. Pushbuttons 74 and 84 may then be released and a circuit to solenoid 64 will be established through lines 12 and 19. A circuit will be established to solenoid 66 through lines 24 and 31. These circuits to solenoid 64 and 66 are maintained while limit switches LS2 and LS4 remain closed from around 140 to 290 of slide movement.

At around 210 of slide movement, limit switches LS1 and LS3 in lines 13 and 25 open. This de-energizes relays R1 and R4 in lines 19 and 31 so that solenoid 64 and 66 remain energized. t

Shortly before opening of limit switches LS1 and LS3 at around 210 of the slide stroke, limit switch LS5 in line 11 closes and remains closed to around 250 of slide movement. However, closing of limit switch LS5 in this mode of press operation does nothing because contact 2R8 of relay R8 is line 11 remains open.

Also at around 250 of slide movement, limit switches LS1 and LS3 again close. Closing of these limit switches at this point also does nothing because contacts 76 and 86 in lines 14 and 26 must be closed in order to energize relays R1 and R4 before another slide stroke can begin. This insures that an operator will not have his hands in the die area during a press stroke and prevents continuous operation if the pushbuttons are stuck depressed.

For continuous operation-of press A, switch 104 is thrown to its continuous position. This closes contacts 106 in line 12, 110 in line 20, 112 in line 24 and 116 in line 32, while opening contacts 108 in line 19 and 1 14 in line 31. In previous control circuits for presses, the press would run continuously once the continuous run switch was thrown and the pushbuttons depressed. This presents a serious danger for an operator who is not aware that the main continuous run switch has been remove or insert a new workpiece within the die area as contacts 1R1 in line 13 and 1R4 in line 25 are open. 1

gized through lines 12, 19 and 17. Relay R5 is 'energized through lines 12, 31, 29 and .7, while relay R6 is energized through lines 12, 31 and 29. Once limit switches LS2 and LS4 open at around 290 degrees of the pressstroke, relays R2, R3, R5 and R6 are also deenergized. The slide will then stop at the top of its stroke. An additional single stroke press cycle is ac complished in the same manner as described.

the slide starts traveling up. If the operator assumed that the presswas in its single stroke mode, he would assume that the slidewould stop in its top position. However, if the circuit is actually in its continuous run mode, and the slide rapidly started down again, the operator might be seriously injured.

In accordance with the present application, an operator must positively hold pushbuttons 74 and 84 constantly depressed through two complete strokes or die closures of the press slide'before it will run continuously without holding buttons 74 and 84 depressed. The operator himself can test the press circuit to see if it is in'its single stroke or continuous run mode simply by holding buttons 74 and 84 depressed. If switch 104 is in its single stroke position, the slide will simply stop at the top of its stroke if buttons 74 and 84 are depressed. lf switch 104 is thrown to its continuous run position, the press slide will continue to cycle if buttons 74 and 84 are held depressed for at least two die closures.

With the press circuit energized, relay R1 is energized through lines 12, 14 and 13. This energizes the contacts for relay R1 in a manner previously described. Relay R4 is also energized through lines 24, 26 and 25. This operates the contacts for relay R4 in the manner previously described. Buttons 74 and 84 are then depressed. This energizes relays R2 and R5 in the manner previously described. Relay R3 is also then energized upon closing of normally open contacts 2R1 'in line 15 and 4R2in line 17. Relay R6 is also then energized through normally open closed contacts 2R4 in line 27 and 4R5 in line 29. The press then begins running in the manner previously described.

Contacts 106 and 2R2 in line 12 establish a holding circuit around limit switch LS1 for maintaining relay R1 energized when limit switch LS1 opens at around 210 of the press stroke. A holding circuit is also established through contacts 112 and 2R5 in line 24 around limit switch LS3 to maintain relay R4 energized when limit switch LS3 opens at around 210 of the press stroke. Therefore, all of relays R1 R6 remain energized when limit switches LS1 and LS3 open with switch 104 in its continuous run condition. When limit switch LS5 closes at around 210 of the press stroke, nothing occurs because normally open contact 2R8 in line 11 of relay R8 is still open. At around 310 of the press stroke, limit switch LS6 in line 23 closes to energize relay R8 through contacts 5R3 and 5R6 which are still closed because relays R3 and R6 are still energized. Energization of relay R8 opens normally closed contact 1R8 in line 28 and closes normally open contacts 2R8 in line 11, 3R8 in line 22 and 4R8 in line 32. if pushbuttons 74 and 84 are now released, the press will stop. This is because there will no longer be a complete circuit to solenoids 64 and 66. Line will be opened by open contact 78 to prevent a circuit through contacts 2R1 in line 15 and 4R2 in line 17 to solenoid 64. Contact 80 in line 18 is open as is limit switch LS2 in line 19. Relay R7 has not yet been energized and contact 1R7 in line 20 is still open. Likewise, contact 88 in line 27 is open and cannot complete a circuit through contacts 2R4 and 4R5 to solenoid 66. Contact 90 in line 30 is also open as is limit switch LS4 in line 31. Normally open contact 2R7 in line 32 is also open because relay R7 has not yet been energized. 7

However, if pushbuttons 74 and 84 are held depressed, limit switch LS6 will open at around 330 of the press stroke. A holding circuit established through contacts 3R8 in line 22, and 5R3 and 5R6 in line 23, maintains relay R8 energized. The press will then immediately begin a second cycle. When limit switch LS5 again closes during the second press stroke, relay R7 will be energized through closed contacts 2R8, 2R3 and 2R6 in line 11. Energization of relay R7 closes normally open contacts 1R7 in line 20, 2R7 in line 32, 3R7 in line 10, 4R7 in line 17 and 5R7 in line 29. Relay 6R7 in line 16 will also be opened.

With relays R7 and R8 energized, along with all of the other relays R1 R6, the press will continue to cycle even though pushbuttons 74 and 84 are released. Holding circuits are established to all of the relays bypassing limit switches LS l-LS6. This also establishes holding circuits to solenoid 64 through lines 20 and 19, and to solenoid 66 through lines 32 and 31.

Relay R2 remains energized through lines 20, 19, 17 and 15. This circuit goes through contact 122 of top stop button 120. Relay R5 remains energized through lines 32, 31, 29 and 27. This circuit goes through contact 124 of top stop button 120. With press in its continuous run mode, depressing top stop button 120 to open contacts 122 and 124 will de-energize relays R2 and R5. The press will then complete that stroke under the control of limit switches LS1 LS6 in the manner described for single stroke press operation and will stop at its top upon opening of limit switches LS2 and LS4 at around 290 of the slide stroke. Before the press can be made to run continuously again, pushbuttons 74 and 84 must be held depressed through more than one press cycle, and preferably for at least two die closures.

With the arrangement described, continuous press operation is accomplished by holding buttons 74 and 84 constantly depressed for one complete press cycle plus around 210 of a second cycle when limit switch LS5 closes. It will be recognized that it is possible to arrange limit switch LS5 in a different manner so that continuous operation is accomplished by holding buttons 74 and 84 depressed for something slightly more or less than 210 of the second cycle or slightly more or less than two complete die closures.

. In general, for the important portions of circuit H which require depression of pushbuttons 74 and 84 for at least two die closures before the press will run continuously, it will be recognized that the circuits through lines 20 and 19 to solenoid 64, and through lines 32 and 31 to solenoid 66, may be termed holding circuits as they include normally open contacts for both relays R7 and R8. In addition, limit switches LS5 and LS6, which energize relays R7 and R8, may be termed locking means for locking in the described holding circuits. Limit switch LS5 may be termed at first limit switch means of thelocking means which energizes a first relay means defined by relay R7. Limit switch LS6 may be termed a second limit switch of the locking means which closes to energize a second relay defined by relay R8 during a second cycle of the press slide or work performing member. These defined first and second relays also have normally open contacts in parallel with limit switches LS5 and LS6 to establish holding circuits to those relays.

Although the invention has been described with reference to a preferred embodiment, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present application includes all such equivalent alterations and modifications and is limited only by the scope of the claims.

Having thus described my invention, I claim:

1.- A control circuit for a machine having a reciprocating work performing member reciprocable between first and second positions, said work performing member moving in cycles defined by movement from said first position to said second position and back to said first position, said circuit including pushbutton means for energizing said machine to reciprocate said work performing member, said pushbutton means being movable between a released position and a depressed position, said circuit including holding circuit means for continuously energizing said machine to continuously reciprocate said work performing member in repetative cycles, said circuit including locking means for locking in said holding circuit means, said locking means being energized by holding said pushbutton means in said depressed position while said work performing member moves through more than one cycle.

2. The circuit of claim 1 wherein said locking means is energized by holding said pushbutton means depressed while said work performing member moves from said first position to said second position at least two times.

3. The circuit of claim 1 wherein said locking means includes first and second relay means and first and second limit switch means, said first limit switch means closing to energize said first relay means during a first cycle of said work performing member, and said second limit switch means closing to energize said second relay means during a second cycle of said work performing member.

4. The circuit of claim 3 wherein said second limit switch means closes to energize said second relay means after said work performing member has moved from said first position to said second position at least two times.

5. The circuit of claim 3 wherein said first relay means has normally open contact means in series with said second limit switch means and said second relay means.

6. The circuit of claim 5 wherein said first relay means has normally open contact means in parallel with said first limit switch means and in series with said first relay means.

7. The circuit of claim 6 wherein said second relay means has normally open contact means in parallel with said second limit switch means and in series with said second relay means.

8. The circuit of claim 3 wherein said first relay means has normally open contact means in parallel with said first limit switch means and in series with said first relay means.

9. The circuit of claim 3 wherein said second relay means has normally open contact means in parallel with said secondlimit switch means and in series with said second relay means.

10. The circuit of claim 3' and further including solenoid means for energizing said machine, said first and second relay means including normally open contact means in series with said solenoid means in said holding circuit means. i

11. The circuit of claim 10 wherein said first relay means has normally open contact means in series with said second limit switch means and said second relay means.

12. The circuit of claim 11 wherein said first relay means has normally open contact means in parallel with said first limit switch means and in series with said first relay means.

13. The circuit of claim 12 wherein said second relay means has normally open contact means in parallel with said second limit switch means and in series with said second relay means.

14. The circuit of claim 13 wherein said second limit switch means closes to energize said second relay means after said work performing member has moved from said first position to said second position a least two times. 

1. A control circuit for a machine having a reciprocating work performing member reciprocable between first and second positions, said work performing member moving in cycles defined by movement from said first position to said second position and back to said first position, said circuit including pushbutton means for energizing said machine to reciprocate said work performing member, said pushbutton means being movable between a released position and a depressed position, said circuit including holding circuit means for continuously energizing said machine to continuously reciprocate said work performing member in repetative cycles, said circuit including locking means for locking in said holding circuit means, said locking means being energized by holding said pushbutton means in said depressed position while said work performing member moves through more than one cycle.
 2. The circuit of claim 1 wherein said locking means is energized by holding said pushbutton means depressed while said work performing member moves from said first position to said second position at least two times.
 3. The circuit of claim 1 wherein said locking means includes first and second relAy means and first and second limit switch means, said first limit switch means closing to energize said first relay means during a first cycle of said work performing member, and said second limit switch means closing to energize said second relay means during a second cycle of said work performing member.
 4. The circuit of claim 3 wherein said second limit switch means closes to energize said second relay means after said work performing member has moved from said first position to said second position at least two times.
 5. The circuit of claim 3 wherein said first relay means has normally open contact means in series with said second limit switch means and said second relay means.
 6. The circuit of claim 5 wherein said first relay means has normally open contact means in parallel with said first limit switch means and in series with said first relay means.
 7. The circuit of claim 6 wherein said second relay means has normally open contact means in parallel with said second limit switch means and in series with said second relay means.
 8. The circuit of claim 3 wherein said first relay means has normally open contact means in parallel with said first limit switch means and in series with said first relay means.
 9. The circuit of claim 3 wherein said second relay means has normally open contact means in parallel with said second limit switch means and in series with said second relay means.
 10. The circuit of claim 3 and further including solenoid means for energizing said machine, said first and second relay means including normally open contact means in series with said solenoid means in said holding circuit means.
 11. The circuit of claim 10 wherein said first relay means has normally open contact means in series with said second limit switch means and said second relay means.
 12. The circuit of claim 11 wherein said first relay means has normally open contact means in parallel with said first limit switch means and in series with said first relay means.
 13. The circuit of claim 12 wherein said second relay means has normally open contact means in parallel with said second limit switch means and in series with said second relay means.
 14. The circuit of claim 13 wherein said second limit switch means closes to energize said second relay means after said work performing member has moved from said first position to said second position a least two times. 